the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Speleothem evidence for late Miocene extreme Arctic amplification – an analogue for near future anthropogenic climate change?
Abstract. The Miocene provides an excellent climatic analogue for near future anthropogenic warming, with atmospheric CO2 concentrations and global average temperatures similar to those projected for the coming century. However, the magnitude of Miocene Arctic warming remains unclear due to the scarcity of reliable proxy data. Here we use stable oxygen isotope and trace element analyses, alongside clumped isotope and fluid inclusion palaeothermometry of speleothems to reconstruct palaeo-environmental conditions near the Siberian Arctic coast during the late Tortonian (8.68 ± 0.09 Ma). Stable oxygen isotope records suggest warmer than present temperatures. This is supported by temperature estimates based on clumped isotopes and fluid inclusions giving mean annual air temperatures between +6.6 and +11.1 °C, compared with -12.3 °C today. Trace elements records reveal a highly seasonal hydrological environment.
Our estimate of >18 °C of Arctic warming supports the wider consensus of a warmer-than-present Miocene and provides a rare paleo-analogue for future Arctic amplification under high emissions scenarios. The reconstructed increase in mean surface temperature far exceeds those projected in fully coupled global climate models, even under extreme emissions scenarios. Given that climate models have consistently underestimated the extent of recent Arctic amplification, our proxy data suggest Arctic warming may exceed current projections. If Arctic warming by 2100 matches our late Miocene estimates, it would have large-scale impacts on global climate, including extensive thawing of Siberian permafrost – a vast fossil carbon store.
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Status: open (until 14 Aug 2024)
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CC1: 'Comment on egusphere-2024-1691', Arthur Oldeman, 19 Jun 2024
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Dear authors,
Your manuscript is interesting and exploring the Miocene climate and its possible similarity to future climate is a relevant endeavour. I have one specific comment on your Miocene future comparison.
You state (L470-475) that the Tortonian saw a similar climate as predicted under a high emission future scenario with atmospheric CO2 levels of 600 ppm. Based on similarities in atmospheric CO2 levels and global temperature anomalies, you proceed to conclude that your ‘findings provides estimates for end-of-century Arctic temperature amplification and precipitation’.
I am not convinced that you can safely make this statement. It assumes to things: 1. CO2 is the dominant driver of (regional) warming, both in the future and Miocene, and 2. Global temperature anomalies are a good proxy for regional temperature patterns and polar amplification. I don’t think that those are a priori assumptions that you can make, and I would like to suggest the authors to explore these assumptions, or find references that support it, before making claims that your findings provide estimates for future Arctic temperatures and precipitation.
That CO2 drives present warming is clear. Next, it is more and more clear that global temperature and CO2 are also connected in the Miocene, something that was not always clear. However, the Tortonian - in fact, the whole Miocene - did not see Northern hemisphere ice sheets. This will have a large effect on the planetary albedo, and with that the global energy budget, resulting in a likely redistribution of heat over the latitudes. This could imply that Tortonian Arctic temperatures and precipitation patterns are in fact not similar to what is projected for the future, regardless of similarity in atmospheric CO2 levels. I am speculating here because I also havent made this analysis, but I find the absence of Northern Hemisphere ice sheets a compelling argument to not automatically assume similarity - or, analogy - between Tortonian and future temperature and precipitation patterns. Hence, I would advise caution with making statements as in L470-475.
Good luck with finishing the manuscript!
Best, Arthur Oldeman
Citation: https://doi.org/10.5194/egusphere-2024-1691-CC1
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